Metal-detectable plastic material

ABSTRACT

A metal detectible plastic material, including a plurality of plastic particles defining a plastic portion and a plurality of high magnetic permeability metallic particles distributed throughout the plastic portion to define an admixture. The plastic particles and the metallic particles are generally the same size and shape, and each respective high magnetic permeability metallic particle has a magnetic permeability of at least 0.0001 H/m. The plastic particles are selected from the group consisting of high molecular mass polymers, thermoplastics, thermosetting polymers, amorphous plastics, crystalline plastics, resin-based materials, and combinations thereof.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application claims priority to then U.S. provisional patentapplication Ser. No. 62/411,894, filed on Oct. 24, 2016, as well as tothen U.S. provisional patent application Ser. No. 62/426,827, filed onNov. 28, 2017, and then U.S. provisional patent application Ser. No.62/532,686, filed on Jul. 14, 2017, and is a continuation-in-part of,and claims priority to, then U.S. patent application Ser. No.14/822,136, filed on Aug. 10, 2015, and issued on Nov. 14, 2017, as U.S.Pat. No. 9,815,743, which was a continuation in part of, and claimedpriority to, then U.S. patent application Ser. No. 13/890,743, filed onMay 9, 2013, and issued on Jun. 6, 2017, as U.S. Pat. No. 9,670,101, andwhich claimed priority to then U.S. provisional patent application Ser.No. 61/644,610, filed May 9, 2012, and to then U.S. provisional patentapplication Ser. No. 61/752,086, filed Jan. 14, 2013, and was also acontinuation-in-part of, and claimed priority to, then U.S. patentapplication Ser. No. 14/192,815, filed on Feb. 27, 2014, which claimedpriority to then U.S. provisional patent application Ser. No.61/770,269, filed on Feb. 27, 2013, each of which are incorporatedherein by reference.

TECHNICAL FIELD

The novel technology disclosed herein relates generally to the field ofceramic materials and, more particularly, to a theoretically densesintered ceramic material that exhibits strong paramagnetic and/orferromagnetic properties.

BACKGROUND

Tooling involved in the production of food and pharmaceuticals istypically metallic. Although ceramic materials have superior compressiveproperties, they are brittle and tend to chip. Thus, ceramic tooling isconsidered unsuitable for use with food and/or pharmaceuticals, sinceceramic chips or fragments are difficult to detect and can contaminatethe foodstuffs and/or pharmaceutical materials. Thus, there remains aneed for ceramic tooling enjoying superior compression strengths alongwith easy detection of chips and fragments for screening and removal.The present novel technology addresses this need.

One tool of particular utility in the pharmaceutical industry is thecompaction die. The compaction die is is an isostatic pressing deviceutilized in the production of tablets utilized in, and not limited to,the following industries: battery, pharmaceuticals, nutraceuticals,cosmetics, confectionary, food, pet food, chlorine and industrialtablets. Such dies are commonly used on tablet presses and the like tocompact powders into green bodies so as to produce tablets or othercompacted shapes.

Thus, there remains a need for ceramic tooling enjoying superiorcompression strengths along with easy detection of chips and fragmentsfor screening and removal. The present novel technology addresses thisneed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a side plan view of a cermet piston assembly according to afirst embodiment of the present novel technology.

FIG. 1B is a side cutaway view of the embodiment of FIG.

FIG. 1C is top plan view of the mandrel portion of the piston assemblyembodiment of FIG. 1A.

FIG. 2A is a front perspective view of the embodiment of FIG. 1A.

FIG. 2B is a partial side cutaway elevation view of the embodiment ofFIG.

FIG. 3 is a side cutaway elevation view of the embodiment of FIG.

FIG. 4 schematically illustrates a typical sintering profile of thecermet material of FIG.

FIG. 5 is a perspective view of the piston assembly of FIG. 1 supportedin a metal-detectible plastic belt.

DETAILED DESCRIPTION

For the purposes of promoting an understanding of the principles of thenovel technology and presenting its currently understood best mode ofoperation, reference will now be made to the embodiments illustrated inthe drawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of thenovel technology is thereby intended, with such alterations and furthermodifications in the illustrated device and such further applications ofthe principles of the novel technology as illustrated therein beingcontemplated as would normally occur to one skilled in the art to whichthe novel technology relates.

The present novel technology relates to ceramic or cermet compositionsthat may be formed into sintered and densified ceramic bodies that enjoythe physical toughness, strength and wear resistance of ceramics whilebeing detectible by conventional metal detection techniques. Thesecermet compositions may then be formed into such bodies asmetal-detectible ceramic tooling or the like, thus offering improvedsafety features by increased ability to detect any small contaminate.

In one embodiment, the cermet composition includes a ceramic matrixphase such as ZrO₂, yttria stabilized zirconia (YSZ), Gd₂O₃, andcombinations thereof, with a metallic phase such as Ni, Fe, Co,permalloy, Mu-metal, and combinations thereof, dispersed therein. Themetallic phase is typically introduced in oxide form for reduction tometallic form during processing, to avoid mixing issues arising fromsignificant density differences as well as metallic species chemicallyinteracting with oxide species at elevated temperatures. Alternately,some or all of the metallic phase component may be introduced asmetallic species.

The metallic phase may be an alloy, and the alloy may be introduced asmetal alloy particles, particles of oxidized alloy, or as oxides of theconstituent metals for reduction and subsequent alloying of theresulting metals. The metallic phase typically has a high magneticpermeability μ of at least about 1×10⁻⁴ H/m, more typically μ being atleast about 1×10⁻³ H/m, still more typically μ being at least about1×10⁻² H/m, and yet more typically μ being about 5×10⁻² H/m. Themetallic phase typically has a relative permeability μ/μ₀ of at leastabout 100, more typically at least about 1000, still more typically ofat least about 10,000, and yet more typically of at least about 20,000,and in some cases, μ/μ₀ may exceed 50,000 or more.

In some specific examples, the metallic phase typically has a highmagnetic permeability μ of at least about 1×10⁻⁴ H/m with a relativepermeability μ/μ₀ of at least about 100, more typically μ being at leastabout 5×10⁻³ H/m and μ/μ₀ at least about 4000, still more typically μbeing at least about 1×10⁻² H/m and μ/μ₀ at least about 8000, and yetmore typically μ being about 2.5×10⁻² H/m and μ/μ₀ 20,000. In somecases, μ/μ₀ may exceed 50,000 or more.

Typically, the matrix and metallic phase materials are provided asprecursor powders, more typically as a homogeneous admixture, with themetallic phase present in sufficient quantity to yield between about 1volume percent and about 20 volume percent metallic particles to theresultant cermet body, with about 80 to about 99 volume percent of thepowder giving rise to the ceramic matrix phase, and with about 1 toabout 8 weight percent of organic additives. A typical composition hasless than 10 volume percent of the powder that gives rise to themetallic phase, with the balance being given to the powder giving riseto the ceramic matrix phase and, optionally a small amount of organicadditives. If the powder giving rise to the metallic phase is areducible material (e.g., a metal oxide), the volume percent of initialprecursor powder is typically appropriately adjusted to compensate forthe loss of the species (e.g., oxygen) that is removed during firing ina reducing atmosphere.

Typically, the matrix phase is a stable, structural ceramic, such asZrO₂, yttria stabilized zirconia (YSZ), Gd₂O₃, or the like, and mayinclude such materials as the various stabilized zirconias,zirconia-toughened alumina, alumina, TiB₂, ZrB₂, HfB₂, TaB₂, TiC, Cr₃C₂,and the like, and mixtures thereof.

The cermet composition may be prepared by any process that yields amonolithic part, typically having a well-blended mixture of the ceramicmatrix phase and the oxide precursor phase, that will yield the metallicphase upon firing in a reducing environment. This may includepreparation by slip casting, extrusion, freezing, and the like. Onetypically selected method is dry pressing, such as uniaxial pressing,cold isostatic pressing, hot isostatic pressing, and the like.

The appropriate powder preparation method is dictated by the selectedmethod for processing the cermet composition. Dry pressing the powdergiving rise to the ceramic matrix phase and the powder giving rise tothe metallic phase are homogenized through mixing/blending to define anadmixture. Additionally, organic additives such as surfactants, bindersand the like may be present in small amounts to aid in powderprocessing, green body formation, and the like. Typically, these organicadditives may be dissolved in a suitable liquid to be gradually added tothe mixed inorganic powders in a shear granulation process. One typicalpowder preparation method includes preparing a suspension of the mixedinorganic powders and organic additives for drying to yield press readygranules.

In the case of an oxide powder precursor for yielding a metal alloyphase (i.e., a metal consisting of more than one element), it ispreferred that the multiple oxide powders be calcined together atsuitably high temperatures to generate a multi-elemental reactionproduct that is subsequently milled to a particle size that isappropriate for subsequent powder processing. Alternatively,predetermined amounts of constituent metals may be mixed and fused, withthe fusion product allow later milled into a metallic powder precursorto yield an admixture.

The homogeneous admixture is then formed into a green body. Typically,the admixture is introduced into a mold and pressed into a green body.In some embodiments, small amounts of binder are introduced to assistthe green body in retaining its shape after formation. The green body isthen sintered at elevated temperatures and under controlled, reducingatmospheric compositions. A majority of the non-matrix metal oxideportion is reduced to yield a sintered cermet body having apredetermined amount of metallic particles dispersed in a sinteredceramic, typically oxide, matrix. In some instances, the admixture isintroduced into a mold and then formed directly into a sintered cermetbody, such as through a hot isostatic pressing (HIP) technique.

Generally, the admixture is heated at one to ten degrees Celsius perminute until a peak temperature between 1400 and 1700 degrees Celsius isreached. Then the admixture is held at this peak temperature for nogreater than four hours. This is followed by a cool down by decreasingthe temperature of the admixture between one to 5 degrees Celsius perminute until a temperature between 1200 and 1400 degrees Celsius isreached. The admixture is to dwell in this temperature range forduration of one to six hours. Then the admixture is to be brought downto room temperature at a rate of one to ten degrees Celsius per minute.The admixture may be processed in powder form, or as pressed into body.The metal particle size and distribution is influenced by the firingtime and temperature. For example, longer firing times and/or greaterfiring temperatures typically yield larger metallic particles.

Once a sintered body is produced, it may be further machined into adesired shape. Further, the sintered body, before and/or aftermachining, may be soaked at an elevated temperature in a reducingatmosphere, such as annealing in hydrogen, to improve its ability to besensed by a metal detector. Other generally appropriate reducingatmospheres may include a forming gas (i.e., hydrogen blended with aninert gas at various ratios), ammonia, vacuum, and combinations of thelike.

In one embodiment, the green body is chemically activated to yield adensified ceramic matrix having a plurality of metallic particlesdispersed therethrough.

In one embodiment, the sintered, densified cermet bodies are formed aspill-making tooling. The pill-making tooling enjoys the benefits ofceramic composition, including compression strength, toughness,durability, corrosion resistance, low coefficient of friction, lowthermal expansion coefficient, and the like. The tooling enjoys theadvantages of the advanced ceramic with the additional ability of beingidentified by conventional metal detection technology.

Other embodiments of the sintered, densified cermet bodies includeequipment and tooling for the processing of foods and beverages, forpharmaceutical manufacture and processing, medical diagnostic devicesand tools, military hardware, weapons, metal blades and cutting tools,industrial tooling and machinery, punches and dies, and the like.

In operation, tooling made from the novel cermet material functionssimilarly to traditional metal tooling, with the exception of typicallyrequiring less lubricant and maintenance. This is advantageous fortooling associated with the production of pharmaceuticals andfoodstuffs, such as pills, vitamins, and the like, as there is anassociated reduction of discoloration (i.e., black marks) of the finalproduct. Further, the novel cermet tooling is typically formed as asingle piece, as contrasted to traditional multipiece tooling (i.e.,metal punch having a ceramic tip), and thus the incidence of attachedtooling pieces becoming dislodged during use is eliminated.

Typically, a production line utilizing the novel cermet tooling willhave metal detectors for detecting and screening tooling chips fromproduct. Typically, metal detectors employ an electric generator forproducing an alternating electric field and a magnetometer for detectingmagnetic fields. The electric generator produces an alternating electricfield which generates eddy currents in electrically conductivematerials; the eddy currents give rise to magnetic fields, which may bedetected by the magnetometer. The tooling chip contaminants containelectrically conductive metallic particles which react to themagnetometer. Chips are thus removed from product upon detection. Insome embodiments, the novel cermet material is sufficientlyferromagnetic as to be magnetically sortable from nonmagnetic product.Further, the novel cermet is advantageous in that, with the properselection of alloy having high magnetic permeability, it has an abilityto be detected at smaller sized particles than ferrous tool steel. Forthe given magnetic permeabilities of this material, as discussed above,tooling chips having diameters of 0.5 mm may be typically detected andmagnetically or otherwise removed, and more typically chips havingdiameters of 0.3 mm may be detected and magnetically or otherwiseremoved.

Moreover, the cermet material is substantially harder and tougher thantool steel. In some embodiments, soft ferrite is used as a stabilizer,supplementing or replacing magnesia, yttria, or like compositions withsoft ferrite and/or permalloy. This can be added to materials such asalumina, mullite, ZTA, or the like and toughen up the material andprovide a low cost hard material with enhanced toughness. Likewise, SiC,graphite, or like other fibers and/or whiskers may be added to provideadditional toughness and strength.

Thus the novel cermet allows for possible abrasion resistance of up to 4to 5 times what is allowed by typical tool steel.

The following example is merely representative of the work thatcontributes to the teaching of the present novel article, and the novelmaterial is not intended to be restricted by the following example.

Example 1

This example relates to a novel method of manufacturing the novelmaterial starting with a Ni/Fe super alloy which is then ground up,milled and mixed with a zirconium ceramic powder to yield a slurry.Wherein the metallic alloy is present in generally sufficient quantitiesbetween typically between about 2 and about 8 weight percent of thetotal (more typically between about 0.5 and about 20 volume percent ofresultant cermet body.) The slurry is then spray dried prior to yield apowder precursor, which may be formed into a green body for sintering.

Generally, the sintering steps occur in oxygen-free conditions and theceramic composition may first be calcined by firing in an ambientatmosphere in order to generally remove any organic additives (binders,dispersants, etc.). Burnout is accomplished by slowly heating theceramic material between the region of 300 to 400 degrees Celsius, thencontinuing to heat the composition until appropriate temperature (on theorder of 900 to 1100° C.) to bisque fire the composition has beenreached, thereby imparting some strength. The bisque fired compositioncan then be heated in a separate step, using the previously discussedheating profile ranges, under vacuum or a reducing atmosphere to convertthe reducible component to a metal while simultaneously sintering thecermet.

Alternatively, the ceramic composition may be fired in a single cycle.The binder burnout portion of the cycle is typically performed in air.Typically, the firing atmosphere remains air until a temperature rangeof between about 900 and about 1100 degrees Celsius, at which point thefiring atmosphere is purged of air and replaced with a reducingatmosphere. Typically, waiting until the temperature range of 900 to1100 degrees Celsius reduces the likelihood of sequential reductionreactions of single metallic elements in a powder that is intended togive rise to a metal alloy phase. Thus, the atmosphere typically remainsas a reducing atmosphere for the remainder of the firing cycle,including the cool down phase. The oxygen content of the sinteringatmosphere may be determined by the amount and nature of the ferritematerial portion of the cermet composition, if any. For somecompositions, microwave sintering is the preferred sintering process.

Once the sintered body is produced, it is typically annealed in hydrogenor other appropriate reducing atmospheres to improve its ability to besensed by a metal detector. The sintered body will typically have adensity of substantially theoretical (in excess of 99 percent, moretypically in excess of 99.9 percent dense), bulk density of about 6g/cc, hardness of about 1100-1500 HV, flexural strength of about 200kPSI, compressive strength of about 2000 kPSI, toughness of 12-14MPa·m^(1/2) (K1c), modulus of 210-230 GPa, and a relative permeabilityμ/μ₀ of about 1000.

FIGS. 1A-3 illustrate one embodiment of the present novel technology, aplunger piston assembly 10 typically utilized in pumps, motors or othersystems that compress solids, fluids, or the like. The plunger pistonassembly 10 generally includes a removable wear sleeve portion 30, amandrel 40, a housing center 50, and a center pin 60. Previously, whenall or part of the piston assembly 10 is worn due to significantcompressive forces inherent in the compaction process, the worn part(s)of the piston assembly 10 is/are discarded and the worn components arereplaced. The plunger piston assembly 10 allows for replacement of thecomponents to quickly put the piston 10 back into service. This may bedone multiple times before the piston assembly 10 has to be replacedwith new parts. Therefore, the piston assembly 10 reduces the cost ofraw materials, labor and transportation costs, as well as the amount oftime the compaction machines are down for repair. The techniquesdescribed herein may be adapted to any of number of compaction toolingapplications. In addition, the piston assembly 10 and replacement methodmay be used in other similar compaction embodiments to allow for the useand refurbishment of various materials, typically the ceramic sleeve 30,in high-friction environments. An advantage of the disclosed embodimentsand methods is the reuse of a highly machined part instead ofreplacement of the same, wherein it is, only necessary toreplace/refurbish the portion of the piston assembly 10 that is worn. Asa result, the life of compaction tooling may be significantly increasedand/or the cost of reworking and refurbishing the same may be reduced.

A piston/plunger assembly 10 generally contains a housing center 50, anelongated tubular body typically formed from a single piece of material,the body having a first end 53, a second end 55, an outer surface 57,and an inner surface 59 that defines a plunger receiving a center pin60. The center pin 60, which is typically disposed inside the housingcenter 50, is typically made from a structural material, such as themu-metal doped YSZ material described above, although various metals andpossibly other materials, such as tool steel or pre-hardened steel, maybe employed and generally includes a first component or a center pinbase 63, which is a generally cylindrical component having an aperture65 in the lower end 67 thereof for controlling the position of thecenter pin 60, and/or affixing the mandrel 40 to the center pin 60, aceramic tip 71 that forms the wear surface of the center pin assembly60. The ceramic tip 71 is attached to the center pin base 73 using amandrel arbor 75, typically made from tool steel, pre-hardened steel, orthe like. As illustrated, mandrel arbor 75 is generally cylindrical, buttypically includes either a tapered head at an upper end 77 thereofmated with tapered hole in ceramic tip 71, or a square head mated withcounterbored hole in ceramic tip 71, so as to provide a positiveengagement between mandrel arbor 75 and the ceramic tip 71.

In the known art, the housing 50, center pin 60, and mandrel 40 weretypically permanently affixed in a manner that individual components ofthe piston/plunger 20 could not be removed or replaced. Thepiston/plunger assembly 10 permits the quick replacement of any of thepiston/plunger components (the mandrel 40, a housing center 50, and acenter pin 60) at any time, without having to tear apart the pump,through the use of a removable sleeve 30. The removable wear sleeveportion 30 is typically made of a structural ceramic material such aswear resistant ceramic oxides, although any convenient material may beselected, and is generally shaped and sized to snugly fit the dimensionsof a standard piston/plunger 20, although the removable wear sleeve 30may be sized and adapted to fit any piston/plunger.

To assemble the plunger piston assembly 10, the center pin 60 istypically inserted into the removable wear sleeve 30. The housing center50 is then attached to the center pin 60 and the mandrel 40 is thencinched down and connected to the center pin 60. This assembly 10 allowsthe piston/plunger 20 to be used until the piston/plunger is worn fromuse. Once the piston/plunger 20 is worn, the ceramic sleeve 30 may beremoved by removing the mandrel 40 with a wrench, thus releasing theceramic sleeve 30. A new ceramic sleeve 30 may then be placed onto thepre-existing mandrel 40 and cinched back onto the center pin 60. The useof such ceramic components enables reworking and replacement of the worntool components. The easy to remove mandrel 40 allows for personnel inthe field to easily remove the mandrel 40 and replace the worn ceramicor high wear sleeve 30 in the field. Alternatively, the plunger pistonassembly 10 may be swapped out and sent back to the manufacturer to berefurbished and reused at a lower cost.

In some embodiments, cermet bodies of the present novel composition areproduced by combining 2-8 weight percent mu-metal powder with a balanceof ceramic matrix powder, such as YSZ, to yield a homogeneous admixture.The admixture is formed into a body having a desired shape by hotisostatic pressing (HIPPING) at a relatively low pressure, typicallybetween 500 and 1000 PSI, and at temperatures in the 900° C. to 1500° C.range in a reducing environment, such as flowing dry H₂ or forming gas.This process yields bodies having densities of greater than 99% oftheoretical (i.e., less than 1% porosity), more typically greater than99.2% theoretically dense (less than 0.8% porosity), still moretypically greater than 99.5% theoretically dense (less than 0.5%porosity); yet more typically greater than 99.9% theoretically dense(less than 0.1% porosity); and still more typically at substantially100% theoretically dense (substantially 0% porosity). FIG. 4 illustratesa typical sintering profile.

In some embodiments, wear sleeve 30 is surrounded by a plastic (such ashigh molecular mass polymers, thermoplastics, thermosetting polymers,amorphous plastics, crystalline plastics, resin-based materials, and thelike) retaining belt or sleeve 31 (see FIG. 5). Retaining sleeve 31offers compression reinforcement to the ceramic or cermet wear sleeve 30while avoiding the potential for rust or like detritus that may form andthen contaminate the pressed bodies. In contrast, a steel sleeve isprone to corrosion and will eventually rust, yielding raised surfacestructures which both weaken the sleeve and cause friction. Such rustspots result in a buildup of powder that will require cleaning andmaintenance, reduce the strength and integrity of the steel sleeve, andcan be easily flaked and chipped off to result in contamination of thepressed bodies. Further, stacking tolerances make for difficulty ininsertion of the wear sleeve 30 into a steel sleeve, making the productdifficult to produce in a high production environment. Further, steel isvery heavy, adding to shipping expense and user fatigue and injury.

A polymer or polymer composite sleeve 31 is lighter, cheaper, and easierto produce and is not prone to the flaking/powder contaminant issuesinherent with rusty metal. Moreover, the insertion of the wear sleeve 30into the plastic retaining sleeve 31 it is more forgiving, reducing theneed for tight dimensional tolerances that are required for shrinkfitting the ceramic in the steel housing. In most cases, the retainingsleeve 31 is molded over the ceramic piece 30. The ceramic sleeve 30typically has radials or groves pressed in the ceramic, allowing theplastic sleeve 31 to hug the ceramic body 30, thus holding the ceramicbody 31 tightly.

In one embodiment, the invention comprises a plastic or polymericcomposition that is detectable by a metal detector. The plasticcomposition is produced by blending polymeric with ferrous and/ornon-ferrous material to make a plastic composite that may then beformed, shaped, and cured or otherwise chemically activated. Thiscomposition can be utilized to fabricate tools for pharmaceutical, food,beverage, medical, or industrial manufacturers, since the chipping ofthese tools will be easily detectable by metal detectors, allowingmanufacturers to enjoy the superior compressive properties, increasedefficiencies, and optimized safety that comes with using ceramic tools.Preferably, the metallic particles loading the plastic composite bodieswill have a magnetic permeability of at least 0.0001 H/ma and a relativemagnetic permeability in excess of 8000. Criteria for the magneticproperties of metallic particles are discussed above. Sleeve 31 istypically formed from such a metal-detectible plastic composition.

In one embodiment, a metal detectible ceramic powder (96% zirconiapowder homogeneously blended with 4% mu-metal powder) is added toconstitute 20%-30% of an admixture, with the balance being polymerpowder material. The admixture is homogeneously blended, and thenformed, such as by molding, into a plastic body of a predetermineddesired shape. The plastic body enjoys increased wear and abrasionresistance and is metal detectible, making it a suitable alternative forretaining sleeve 31 applications, and even some tooling applications,such as plunger assembly 10 and/or die 30 applications.

Example 2

YST powder was mixed with oxidized mu-metal alloy to yield a homogeneousadmixture having 4 weight percent oxidized mu-metal. The powder waspressed into a green body and calcined at 600° C. for 8 hours to debindand remove the oxygen from the oxidized mu-metal. The temperature wasramped to 1400° C. and the calcined body was soaked at 1400° C. for 2hours to sinter. The sintered body was hot isostatically pressed at 900PSI in a reducing atmosphere (5% hydrogen gas), after which the body wasannealed at 1120° C. for 4 hours, and then ramped to room temperatureover 5 hours. The body had a density of substantially theoretical (inexcess of 99.9 percent dense), hardness of about 1450 HV, flexuralstrength of about 200 kPSI, and a relative permeability μ/μ₀ of about1000.

Example 3

YST powder was mixed with mu-metal alloy and a binder to yield ahomogeneous admixture having 3 weight percent mu-metal. The admixturewas heated in an oxidizing atmosphere to oxidize the mu-metal. Thepowder was pressed into a green body and plasma sintered at 1400° C. ina reducing atmosphere (dry H₂) for 10 minutes to remove binder and alsothe oxygen from the oxidized mu-metal and sinter the body. The sinteredbody was allowed to cool to room temperature with the furnace (naturalcool down). The body had a density of 99.5 percent theoretical, ahardness of 1470 HV, flexural strength of 204 kPSI, and a relativepermeability μ/μ₀ of 2500.

Example 4

YST powder was mixed with mu-metal alloy to yield a homogeneousadmixture having 5 weight percent mu-metal. The admixture was heated inan oxidizing atmosphere to oxidize the mu-metal. The powder was pressedinto a green body and plasma sintered at 1400° C. in a reducingatmosphere (dry H₂) for 20 minutes to remove the oxygen from theoxidized mu-metal and sinter the body. The sintered body was allowed tocool to room temperature with the furnace (natural cool down). The bodyhad a density of 99.2 percent theoretical, a hardness of 1450 HV,flexural strength of 200 kPSI, and a relative permeability μ/μ₀ of 2500.

While the metal, typically mu-metal, composition is typically held under20%, compositions are envisioned with sufficient metal or mu-metal phasesuch that the resulting sintered bodies exhibit metallic electricalconductivity. Such bodies would have contiguity or quasi-contiguity ofthe metallic phase, and would be able to participate in screening ofelectromagnetic energy. For example, a functioning Faraday cage may beconstructed of high-metal phase cermet pieces.

Bodies formed as described above, particularly those sintered inhydrogen, exhibit the characteristics of having smooth andquasi-polished or polishable surfaces, require substantially lesslubrication than metal counterparts, wear evenly with substantiallyreduced chipping and pitting (than metal or conventional YSZcounterparts). Tooling for pressing pills benefits from high wearresistance, reduced pitting, chipping and rut erosion, reducing and/oreliminating retention of surface material and potential for bacterialcontamination.

In one embodiment, the compaction die is utilized on a tablet press andfilled with powder with scraper blade and suction from lower punch.Upper and lower punches or like structures may tamp the powder in thedie to yield a green body, after which the lower punch lifts and ejectsthe tablet or body from the compaction die. The parameters of thisprocess are varied (fine-tuned) depending on the equipment and desiredfinished product.

In the prior art, the compaction die is typically inserted into andsupported by a steel retaining belt or ring, the belt having been cutand machined to yield an inner diameter (ID) dimension having very tighttolerance and having a very smooth machined and symmetrical surface. Theceramic or cermet sleeve is also formed to have a very specific outerdiameter (OD) dimension with a smooth surface. The metal is then heatedand expands, and at this time the ceramic sleeve is inserted in thesteel belt or housing (shrink fit). The inside dimension in the ceramiccan be core drilled prior to the shrink fit or after. If done before orafter the ceramic may crack due to the pressure from the metal shrinkingtightly around the ceramic. The required force to hold the ceramicvaries per industry. Final machining is then required to remove excessmetal and ceramic and bring the die assembly to customer specification.Stacking tolerances and proper surface parameters make this productdifficult to manufacture in a high production environment. Anotherdrawback of the prior technology is that the steel is reactive andtypically develops rust spots, which manifest as raised surface featuresand thus have the potential to cause friction. This typically gives riseto a buildup of powder, and increases the need for frequent cleaning andmaintenance. The rust also reduces the strength and integrity of thedie, is easily chipped, and causes contamination. In addition, the steelbanding makes the die assembly very heavy for both the operator to useand the manufacturer to ship.

In operation of this embodiment, a cermet die assembly is inserted intoand supported by a polymeric or plastic housing. The insertion processis much more forgiving and reduces the need for tight specifications forshrink fitting the ceramic or cermet die assembly into the housing. Thecermet die assembly requires less stringent dimensional tolerances(i.e., bigger window) as the plastic support belt or housing may bedirectly molded over or onto the ceramic. The ceramic or cermet dieassembly typically includes radials or groves formed thereinto forengaging the plastic housing so that the housing “hugs” the cermet dieassembly for a glove-like fit. Production time and difficulty are bothreduced, thus reducing the per-part cost as well. The product failure orreject rate is likewise reduced significantly, along with the risk ofcatastrophic failure when the die assembly is in use. Further, theweight of the supported cermet die assembly reduced to about one-half,more typically to about one-third, of that of its steel bandedcounterpart.

In many embodiments, the cermet material is sufficiently electricallyconductive that the cermet bodies may be machined via electric dischargemachining (EDM) techniques with high precision and at room temperature.EDM machinability is significantly quicker and less expensive thantraditional grinding techniques for yielding high-precision ceramicworkpieces. In particular, wire-cut EDM techniques may be applied toyield intricate features in the cermet body.

The relatively high, metallic or quasi-metallic electrical conductivityof the cermet powders and bodies makes them uniquely qualified forservice as both EMF and physical or structural shielding for electronicdevices, personal use (such as EMF filtering earplugs or helmets), andthe like. Further, the material may have an electrically insulatingsurface or portion when combined with a layer of insulating material,such as alumina or mullite. Such bodies could be formed as unitarypieces or as multipiece composites.

The sintered, EDM-friendly body will typically have a density ofsubstantially theoretical (in excess of 99 percent, more typically inexcess of 99.9 percent dense), bulk density of about 6.1 g/cc, hardnessof about 1150-1250 HV, flexural strength of at least about 200 kPSI,compressive strength of about 2000 kPSI, toughness of 10-14 MPa·m^(1/2)(K1c), modulus of 270-290 GPa, and a relative permeability μ/μ₀ of about1000.

Green bodies formed from cermet powder precursors via CIP, HIP, hotpressing, injection molding, casting or like processes may be formed tonear-net shapes, often without the need for binders. These green (andtypically binder-free) bodies may be precision machined into complexshapes as green bodies, calcined bodies or fully dense sintered bodiesvia EDM machining, taking advantage of both the toughness and hardnessof the cermet materials and their bulk electrical conductivity forprecision machining and polishing. The lack of a binder requirementlikewise typically reduces both shrinkage and calcination/sinteringcycle time.

The cermet bodies tend to have slick, smooth surfaces that areself-lubricating, giving punches and dies the advantage of requiringless, if any, lubricant that might otherwise contaminate powders andgreen bodies, as well as reducing the tendency of powders to stick topunch and die surfaces. Cermet tools thus require less frequentmaintenance than do steel counterparts.

Metal leaching tests have yielded results indicating that the novelcermet material loses substantially less metal than tool steel underASTM Method C738-94 test conditions.

TABLE 1 YSZ body Ni: 0.00 ng Ni/mm² Fe: 0.04 ng Fe/mm² Mu-metal Cermetbody Ni: 1 ng Ni/mm² Fe: 1 ng Fe/mm² Tool Steel body Ni: 30 ng Ni/mm²Fe: 70 ng Fe/mm²

While the novel technology has been illustrated and described in detailin the drawings and foregoing description, the same is to be consideredas illustrative and not restrictive in character. It is understood thatthe embodiments have been shown and described in the foregoingspecification in satisfaction of the best mode and enablementrequirements. It is understood that one of ordinary skill in the artcould readily make a nigh-infinite number of insubstantial changes andmodifications to the above-described embodiments and that it would beimpractical to attempt to describe all such embodiment variations in thepresent specification. Accordingly, it is understood that all changesand modifications that come within the spirit of the novel technologyare desired to be protected.

I claim:
 1. A metal detectible plastic material, comprising: a pluralityof plastic particles defining a plastic portion; and a plurality of highmagnetic permeability metallic particles distributed throughout theplastic portion and formed into a unitary body; wherein each respectivehigh magnetic permeability metallic particle has a magnetic permeabilityof at least 0.0001 H/m and a relative permeability of at least 8,000;wherein the plastic particles are selected from the group consisting ofhigh molecular mass polymers, thermoplastics, thermosetting polymers,amorphous plastics, crystalline plastics, resin-based materials, andcombinations thereof; wherein the unitary body is a retaining sleeve.